It isn't just the rough outline of Star Destroyer, Tatooine, Death Star, etc; it is the details in each.
There was a specific effort by George and the rest of the crew to make RoTJ bigger than Star Wars. Jabba's Palace would have more creatures than the cantina. The musical number would be bigger. The space battle would be faster and more intense. The lightsaber fight at the end would be bigger with aerobatics and stunts.
Jedi was definitely a re-hash of Star Wars.
Not that I am saying that it is bad that it is a re-hash. If you want to gripe about something, you will find a reason to do it. If it is similiar, then it is a re-hash; if it is different, then it isn't Star Wars.